A spokesman from Which? said: "If you own this seat, or know anybody who has this seat, we advise you to replace it as soon as possible due to a serious failing we uncovered in our car seat crash testing."

The seat, which is on sale at Argos, was put through crash tests causing parts of the seat to be ripped off. In a real crash the child would be at risk of colliding with the seat in front because of the failure of parts of the seat.

Argos told the Mail that the seat had been removed from its catalogue in July, but a small amount of remaining stock would still be sold as the seat passes standard European safety tests.

Which? safety tests are more stringent than the standard European tests - including a 'slide test' and a front-on crash at a higher speed.

The seat has passed official EU regulatory tests to be sold as suitable for children from birth up to 18kg, and was marked as ECE R44/04 approved.

The car seat is no longer being produced, but Argos confirmed it was still selling any existing stock it had as it had met the standard European safety regulations.

Which? said second-hand products are available on websites such as Gumtree and Ebay and advised against buying the seat or any second-hand car seats.

The seat scored the lowest ever test score of zero per cent in the more demanding, independent crash tests, which are conducted at higher speeds and forces than the current UK standards require.

Which? branded the seat a 'don't buy' because the shoulder parts of the harness were ripped out of the plastic seat shell as it broke under the force of the crash tests.

A spokeswoman at Argos said: "Customer safety is our top priority and we were extremely concerned to hear of the issues raised in the Which? Report regarding the BabyStart Multi Recline Car Seat.

"Following an internal investigation alongside our supplier TeamTex, we can confirm that we have had no issues or customer complaints in relation to this product.

"The BabyStart range is sold exclusively at Argos and we stopped selling this particular car seat in July as part of our normal new range process, however a small number of car seats are still available."